In a conventional injection machine, as shown in FIG. 1 for example, a screw 1 is rotated through reduction gear 5 rotated by a motor 4 in order to melt and inject the plastic material from a hopper 6.
The material supplied from the hopper 6 into a cylinder 2 is plasticized by the shearing heat from the rotation of the screw 1 and the heating from an external heater 7, and is accumulated in the cylinder 2. The plasticized molten material is injected by the advancing motion of the screw 1 through the operation of an injection cylinder 3.
In such conventional example, since the heater temperature elevation takes a long time, power must be supplied to the heater 7 about 20 to 30 minutes before start of injection, which is often a serious disadvantage in interlocked or synchronized operation between a forming machine and an assembly line.